1. Field of the Invention
This invention relates to devices for preventing cold induced reductions in the dexterity of the extremities of divers and others working in wet or submerged conditions. More particularly, this invention relates to boots, sleeves, leggings and gloves which can heat or maintain at a level temperature the total volume of a persons extremities using radio frequency (RF) energy.
2. Description of the Prior Art
It has been well documented that the environmental factor of cold water is a prime cause of impaired diver performance (Bachrach et al., "Human Performance Underwater", Dividing Medicine (R. H. Strauss, ed.), pp. 183-196, Grune et al., New York (1976); Curley et al., "Wet-suited Scuba Diver Performance in 5.degree.-25.degree. C. Water", Report NMRI 81-51, Naval Medical Research Institute, Bethesda, Md. (1981)). A reduction or loss of a persons dexterity typically occurs at finger temperatures below about 15.degree. C. (Clark, "The Limiting Hand Skin Temperature For Unaffected Manual Performance In The Cold", J. Appl. Physiol. 45, pp. 193-194 (1961); Dusek, "Effect of Temperature on Manual Performance", Protection and Function of the Hands in Cold Climates, F. R. Fisher, ed., pp. 63-76, National Academy of Sciences, Washington, D.C. (1957)). Purely passive thermal hand protection is self defeating because it necessitates the use of bulky gloves or mittens and precludes the full usefulness of the hands.
To date, active thermal protection of the extremities has involved surface-applied heat such as warm water or direct electrical current to heat a resistive wire. Surface-applied heating methods tend to be inefficient in cold water because of large conductive heat losses and because of the thermal limitations caused by skin burning. Radio frequency (RF) energy has received little attention for use in extremity warming even though the deep-heating properties of helical RF coils for tumor therapy and hypothermia resuscitation have been demonstrated (Olsen, "Reduced Temperature Afterdrop in Rhesus Monkeys With Radio Frequency Rewarming", Aviat. Space Environ. Med., 59, pp. 78-80 (1988); Olsen et al., "Hypothermia and Electromagnetic Rewarming in the Rhesus Monkey", Aviat. Space Environ., 55, pp. 1111-1117 (1984); Ruggera et al., "Development of a Family of RF Helical Coil Applicators Which Produce Transversely Uniform Axially Distributed Heating in Cylindrical Fat-muscle Phantoms", IEEE Trans. Biomed. Eng., BME-31, 98-106.5-7 (1984)).
Systems exist, such as hunting socks, which provide heat to the skin surface by means of a DC current flowing through resistive wire. These surface heaters are inefficient often requiring bulky, high energy power sources. In addition, surface heaters can cause surface burns if the temperature is raised sufficiently to warm the extremity core. A system that deposits energy within the volume of an extremity rather than at its surface is more efficient in maintaining a diver's manual dexterity without the need for a prohibitively large and bulky electrical power source.
In U.S. Pat. No. 4,685,462, the inventor herein, R. G. Olsen, describes a jacket-type device which utilizes a torso-encircling resonant coil irradiation system to resuscitate hypothermic subjects. The torso device was found to operate successfully in an air environment. Water between the windings of the coil was found to interfere with operations. There was a need for an active warming device which is operable under submerged or near submerged conditions.